Metal carboxylate antioxidants for fluoroesters



United States Patent 3,262,881 METAL CARBOXYLATE ANTKOXHDANTS FOR FLUQROESTERS Harold Ravner, Accokeelr, and Carter 0. Timrnons, ()xon Hill, Md, assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed May 31, 1963, Ser. No. 284,753 3 Claims. (Cl. 252--37.2)

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to fluoroesters, more particularly to improvement in the oxidation stability of fluoroesters at high temperatures.

Developments in military and industrial equipment have presented an increasing demand for lubricants and hydraulic fluids which can meet severe operational requirements. Among such requirements is oxidation stability at high temperatures.

Fluid neutral esters of omega-hydroperfluoroalkylcarbinols and saturated aliphatic hydrocarbon polycarboxylic acids have been heretofore suggested as a source of potential high temperature lubricants and hydraulic fluids. As a class these esters lack the necessary oxidation stability which would allow their use as lubricants or as hydraulic fluids at temperatures in the range of about 400 to 500 F.

It is an object of the present invention to improve the oxidation stability of fluoroesters of the aforesaid class whereby to provide new high temperature lubricants and hydraulic fluids.

We have found metal carboxylates hereinafter more fully defined to be antioxidants which impart an exceptional degree of oxidation stability at elevated temperatures in the range of about 400 to 500 F. to fluid neutral esters of omega-hydroperfluoroalkylcarbinols which have from 5 to 11 carbon atoms and saturated aliphatic hydrocarbon di-, tri-, and tetracarboxylic acids which have from 3 to 9 carbon atoms in the hydrocarbon group.

The metal carboxylates constituting the antioxidants of the present invention are divalent metal salts in which the metal is barium strontium, copper, cobalt, nickel, titanium, cerium or ytterbium and the acid portion is the residue of two moles of a monocarboxylic acid of the formula R'COOH, or of one mole of a dicarboxylic acid of the formulas (CGOH) and R"(COOH) The metal carboxylates have the general formulas:

wherein R is a univalent and R a divalent hydrocarbon radical which may be saturated aliphatic, phenyl-substituted saturated aliphatic or of the benzene series, or a perfluoroalkyl or perfluoroalkylcarbalkoxyl radical, and M is a metal as defined above. Copper is a preferred metal in the antioxidant carboxylates of the invention. Illustrative of the aforedefined metal carboxylates as antioxidants for the fluoroesters are barium, strontium, copper, etc., acetates, butyrates, isobutyrates, caprates, laurates, stearates, hexahydrobenzoates, phenylacetates, Z-methylphenylacetates, S-phenylcaproates, 8-, 9-, and l0-phenylstearates, etc.; perfluoroundecanoates, 1H,1H, 7H-dodecafluoroheptyl-3-methyl glutarates, lH,lH,5H- octafluoropentyladipates and sebacates, etc.; oxalates, malonates, succinates, glutarates, 3-methylglutarates, adipates, sebacates, undecanedioates, 1,2-cyclobutane dicarboxylates, camphorates, hexahydrophthalates, phenylmalonates, phenylsuccinates, phthalates, etc.

The metal carboxylates of the foregoing formula are relatively insoluble in the fluoroesters. They are effective in small concentrations, on the order of from about 0.05 to 0.5% by weight, preferably on the order of from about 0.1 to 0.2% by weight, to impart a high order of oxidation stability to the above defined fluoroesters at temperatures in the range of from about 400 to 500 F. The threshold temperature for antioxidant activity for the metal carboxylates is about 400 F. Below this temperature, the fluoroesters are in themselves oxidation stable. The oxidation stability imparted to the fluoroesters will vary with the particular metal carboxylates and fluoroesters and will be higher at the lower temperatures in the aforesaid range since the oxidative stress is less at the lower temperatures. The metal carboxylates may be added directly to the fluoroesters or a by-pass system may be employed which contains a confined mass of the metal carboxylate (powder) through which the fluoroester flows in contact before returning to areas of lubrication.

The fluid neutral fluoroesters With which the present invention is concerned may be prepared in known way as described in Ind. Eng. Chem, 48, 445 (1956), from the omega-hydroperfluoroalkylcarbinols of the general formula:

H CF CF CH OH wherein n is an integer from 2 to 5 and aliphatic poly- .carboxylic acids of the general formula:

. are those described in Ind. Eng. Chem. 48, 445, above,

for example, bis (1H,lH,5H-octafluoropentyl)- and his (1H,1H,7H-dodecafluoroheptyl) 3-methylglutarates, bis (1H,lH,5H-octafluoropentyl) adipate and sebacate, tris (1H, lH,5H-octafluoropentyl) tricarballylate, etc.

The antioxidant activity of the metal carboxylates may be evaluated in terms of increase in viscosity and rise in the neutralization number of the fluoroesters. The amount of fluoride evolved from the fluoroesters may also be an evaluating factor. The lower the value for these factors, the greater in general the oxidation stability imparted to the fluoroesters by the metal carboxylates at a given temperature in the aforesaid range. Depending upon the conditions of service use, all or less than all of these factors may govern in the selection of the fluoroesters on the basis of oxidation stability at temperatures within the aforesaid range. Thus, where the acid developed in the fluoroester is not a corrosion problem, either by virtue of the acid in itself being non'corrosive or the metal parts with'which the fluoroester and developed acid come into contact are acid resistant, rise in the neutralization number can be of minor significance. Similarly, evolved fluoride also can be of minor significance where means are provided for venting of the evolved fluoride from an engine or other system in which the fluoroesters are employed.

Increase in viscosity and rise in the neutralization number of the fluoroesters and the amount of fluoride evolved therefrom on heating the fluoroesters to temperature in the aforesaid range after addition of the metal carboxylates thereto may be determined by use of the dynamic oxidation test procedure and apparatus described in Ind. Eng. Chem., 39, 491 (1947). In this test, the samples of the fluoroesters with the added metal carboxylates are contained in cylindrical cells made of bo-rosilicate glass. The control is a like volume of the fluoroester but without the addition of the metal carboxylate thereto. Each of the cells is equipped with a water-cooled condense-r fitted to the top thereof and has a rubber hose connected from the condenser to a separate water trap. Sealed to the upper wall of each of the cells is means for delivering 1 DYNAMIC OXIDATION TE ST Bis (1H, 1H, 7H-dodecafluoroheptyl)-3-methylglutarate Additive a Viscosity Neutralization Fluoride Weight Temp. F.) Test Period Increase Number Evolved (Percent) (hours) at 100 F. Increase mg. F/gm.

(Percent) Mixed Fluoroalcohol Camphorate 2 0.03 437 168 7 0.84 0.27 2 0.03 437 168 2. 7 0. 06 0.2 0. 5 437 168 31 1. 5 Nil 482 72 Gelled 0. 5 482 72 111 6 Nil 0. 5 482 72 1. 6 1. 7 2 0.1 482 72 13 1. 6 0. 1 482 72 20 1. 4 0.1 482 72 7.5 5.7 1. 9 0. 5 482 72 13 11 2. 2 0.1 482 72 32 7. 5 2. 4 0.1 482 72 46 15 1.0 0.1 482 72 135 14 2. 8 0. 1 482 72 141 13 1. 4 0. 1 482 72 43 14 2. 4 0. 5 482 72 23 10 2. 2

1 Not determined. 2 Concentration of metal. Additives Code:

Copper (toluate) Barium toluate.

Nickel (benzoate) Cobalt (benzoatefi.

Ti 9 Titanium (toluate) Yb 10 Ytterbium (toluatefi.

Sr 11 Strontium toluate.

bubbled air into the bottom of the fluoroester samples in the cells. The cells containing the fluoroester samples with added metal carboxylate and the cell with the control sample are placed in snugly-fitting holes in an electrically heated Duralumen block which is thermostatically controlled to hold at the test temperature i0.5 F. Clean dry air, free from CO is bubbled through the heated fluoroester samples in the cells at a predetermined volume and rate. The eflluent gases from each of the cells which have passed through the individual associated condenser are led into the water trap provided therefor and the fluoride content of the trap liquid determined by the lead chlorofluoride method. The amount of evolved fluoride is reported as mg. of fluorine per gram of the fluoroester. The viscosity in centistokes at 100 F. and the neutralization number of the fluoroesters are determined before and after the test. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize the fluoroester. 1 Indicative of the oxidation stability which can be imparted by the metal carboxylate antioxidants of the invention to the fluoroesters of the aforesaid group at temperatures in the range of about 400 to 500 F. are the results obtained with his (1H,lH,7H-dodecafiuoroheptyl) 3-methylgl utarate and with commercial (Du Pont Company) mixed fluoroalcohol camphorate from the complete esterification with camphoric acid of mixed C C and C fluoroalcohols of the formula H(CF CF CH OH in which the ration of the fluoroalcohols was approxi- 1 Copper (lI-I,1H,7H-perfluoroheptyl-3-methylglutarate) Copper (phenylstearatefi.

Copper (perfluoroundecanoatefl.

Cerium (1H,1H,7H-perfluoroheptyl-3-methylglutarate) The foregoing results demonstrate the capacity of the metal carboxylates as defined herein to provide a marked increase in the oxidation stability of the fluoroesters herein described at temperatures in the range of 400 to 500 F. The test results show the copper carboxylates to be generally superior in retarding increase in viscosity of the fluoroesters in the indicated temperature range and the copper perfluoroundecanoate to completely prevent evolution of fluoride at temperatures up to at least 482 F.

While the invention has been described herein with reference to certain specific embodiments thereof, it ohviously may be otherwise practiced without departing from the spirit or scope thereof and, accordingly, such specific embodiments are intended by way of illustration and not in limitation except as may be defined in the appended claims.

What is claimed is:

1. A composition comprising a fluid neutral ester of a fluoroalcohol of the general formula:

H (CF CF CH OH wherein n is an integer from 2 to 5 and an aliphatic polycarboxylic acid of the general formula:

wherein n is an integer from 2 to 4 and R is a saturated aliphatic hydrocarbon group having from 3 to 9 carbon F #3 atoms and a metal carboxylate of the group consisting of wherein R is an univalent and R a divalent hydrocarbon radical of the group consisting of univalent and divalent saturated aliphatic and phenyl-substituted saturated aliphatic hydrocarbon radicals, univalent and divalent hydrocarbon radicals of the benzene series, perfluoroaikyl and perfiuoroalkylcarbalkoxyl radicals, and M is a metal of the group consisting of barium, strontium, copper, cobait, nickel, titanium, cerium and ytterbium, in amount sufiicient to increase the oxidation stability or the fluid neutral ester at temperatures in the range of from about 400 to 500 F.

2. A composition as defined in claim 1, wherein the metal in the carboxylate is copper.

3. A composition as defined in claim 1, wherein the metal carboxylate has the general formula:

(R-COO) Cu in which R is a univalent hydrocarbon of the benzene series. References Cited by the Examiner UNITED STATES PATENTS 2,180,697 11/1939 Vobach 25237.7 2,472,503 6/1949 Van der Minne 252407 2,560,542 7/1951 Bartleson et al 25237.7 2,840,593 6/1958 Somrners et al 252546 2,921,957 1/1960 ORear et al 25254.6 3,017,361 1/1962 Morris et al 25276 3,124,533 3/1964 Metro et a1 25254.6

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner. 

1. A COMPOSITION COMPRISING A FLUID NEUTRAL ESTER OF A FLUOROALCOHOL OF THE GENERAL FORMULA:
 3. A COMPOSITION AS DEFINED IN CLAIM 1, WHEREIN THE METAL CARBOXYLATE HAS THE GENERAL FORMULA: 